Electrolytic production of polyhydric alcohols



Patented July 24, 1951 sELETCTROLEC-TIC:PRODUCTION OF w POLYHHEDRIC ALCOHOLS Ch'erryl'L; Emerson, 2b., Newton Highlands, Masa,

"assignorto' Emerson & Coming *ton,-Mass., a partnership Application July 28, 1948;

-N'o Drawing.

Company Bos- Serial No. 41,172

i 1 gimiis invention relates to the iproductionnf isoibitolior other ipolyhydric alcohols bytheelebltrolyticireduction of glucose or other "sugai'stin l bufflered acid solution.

It "has been appreciated for many years that 12 clam s. (o1. 204 7v) t the electrolytic "production of sorbit'o'l fromJg'lu- (nosemay be carried out in aqueous acid solution with. considerable advantage in respect to yield one quality over employment of an alkaline soluti'on. Informationas to thestaitus of the'gprior ;art will be found .in the' Creig'hton Patent 1,990,582 and "Hales Patent"2,3 ,"2 1 3 (if the] Atlas LRowderCompany. There are,however, serious gdiificulties in the way of c'ontrolling'the .pH "of liacid electrolytes. For example, slight "changes :ineoncen'tration of the electrolytes will result "inlarge pl-I changes, which infturn make very .diificultfthe maintenance of good reduction cont-diti'ons. Furthermore, Ilow temperatures must be .Ltigidly maintained if "high qualityma terialisfto I b'eproduced.

,I have discovered a simple; inexpensive and iireliable process of producing sorbitol and other ie alcoholsl by electrolytic reduction .of glucose and other sugars in -acidisolution which solves the problem of control and leads-among iother things, .to the complementary advantage of the employment of much highertemperature Iley'els'in operation. Myunovel process is characterized by the employment of an acidcathodic :Solution of an anionic .bul'fer salt and'the sugar nto be reduced. The bulk catholy'te .pI-I may be maintained at any point "between '-'land 2.5; the

ianolyte pH is normally verylow.

.Myprocess isalso characterized by the emtployment of i a permeable diaphragm separating anode and cathode compartments, ofmsuch .po-

grosity and permeability that the current density employed can be used to set up a voltage gradient through the diaphragm suiiicient to induce tt'he' phenomenon of ielectroendosmosis. Elec'tro- "endosmosis is the bulk movement of liquid from one electrode to the other through the diaphragm underthe influence orthe electriic-current. ."Bulk movement may be controlled by varying the current i density. I can, therefore,

. i use electroendosmosis as an exceptionally effective and precise method of controlling .pI-I. Since ,l' also employ an acid catholyte buffered by the alkali salt of a weak acid, I' am able to the iprocess without attention once the proper confditio'ns are established and Without substantial :j'changein the H orthe catholyte or departure "firom'ideal conditions. u more into detail; I .employ jat' 'the "bliilfer :z I i in my process an alkali salto'faweak a'didlfor example, sodium aci'd phosphate or sodium acid carbonate. The phrase "phosphate anion -is used herein to include any or allof the group of anions consisting or HzPOr, I-IPOr P'Or or For and its polymers, or g. ZPiOw My 4 while carbonate -anion is used toinclude any or both of theanio s of the group -'consistlng of HCOB, and Cos "Q My process is 'furth'er' oharacterizedbythe positive steps which ar'eta'ken to insure the rermation and maintenance of a thin alkali fllm a't the cathode surface. Phe sugar on passing through the alkalifilmtdthe cathode surface is converted to the eno'licform in which tor-mart may "be reduced to "the corresponding p'olyhydric alcohol by hydrogen liberated at the cathode mains acid and the sugar in non-enol'icifomn.

"By this procedure or establishing an-alkalirffilm at the cathode Surface while the bulk eatholyrte remains in rbuireredacid solutionat any neared pH between 7 f0 and 295, I} develop conditions under which the sugar f itself will ac't ias :amea

fective "depolarizing agent. The establishment or the thin alkali film in the presence'iofwa bifik "plyin'g aliq'iiid alkalLsuch sodiumthydroxide,

"invention is that it permits continued operation at "a high temperature level without-upsetting the reducing conditions and without-adversely affecting normal high "quality "of thew/product.

Where sodium sulphate has; been employedrhs the electrolyte, it has been 'foundz'necessarymo remove he'at" *fr'om the cell by irefri'gerationuzzin order to maintain the controldor highuality production. For instance, at oatholyte temperatur'e of close to 20 C. is needed Witihnsodiuin (S111- phate electrolyte "if a high qualityiproduot: ism'to be produced. "in myprocesspron :the contrary, temperature levels *of 40 C., m'ay be utilized "with good results. Furthermore: EpI-I :controlwot a solution containing sodium sulfate hast-ween generally found to 'be an extremely delicatei'matter requiring constant attention. By employtng a catholyte 'bufferedwi-th "the alkali salt or 'a wealk acid and 'by making"use of the phenomenonwi ot electroendosmosis, I am able to run the "process Without attention and without substsmtlal fc'han'ge in thepH "oi the catholyte. I abelieve ithat this is due to the fact that sodium sulfate (the only electrolyte salt found usable in acid solution in prior processes) is the salt of a strong acid and a strong base and hence offers no buffering action comparable to that of anionic buffers, such as the sodium phosphates or carbonates, which are salts of weak acids. This may mean that when using sodium sulfate a relatively thick alkali film forms at the cathode surface with the bulk catholyte at low pH. A thick alkaline film at high temperature tends to degrade the glucose diffusing through it toward the cathode surface. Moreover, such a film will be inherently more unstable due to the lack of buffering action in the catholyte. For example, the addition of acid to the catholyte as previously suggested greatly disturbs the film.

Another real and important advantage of my process accrues from the use of the phenomenon of electroendosmosis. By its proper use and control I can nullify the effects of ionic movement inherent in electrolytic processes. Furthermore, I can neutraliz'ethe diffusion normally set up as sides of the diaphragm. It can be seen at once that not only is this an excellent expedient for controlling pI-I precisely but that it can also be used to eliminate completely the diffusion of 7 solution of glucose.

,a result of concentration differences on the two glucose from cathode to anode compartment.

Thus high concentrations of glucose can be used vin the catholyte without loss of yield due to oxidation in the anodecompartment.

A further advantage arising from the use of my process is that the anions of the buffer salts which -I use are irreducible at the cathode surface under the conditionsemployed andhence have no tendency to upset reduction by causing a deposit upon the cathode. In the case of acid solution of so- :dium sulfate, however, the sulfate anion is quite.

susceptible to reduction. Any disturbance of the alkaline film at the cathode surface, such as occurs when acid is added to the catholyte for pH control, will result in hydrogen reacting with the sulfate ion in acid solution. There follows a sulfide deposit on the cathode surface which if allowed to grow enough will completely stop reduction. This has been experimentally demonstrated. Likewise, the use of mixing has been found impossible in a sulfate process since it is accompanied by complete disturbance of the alkali film at the cathode surface and shortly thereafter by cessation of reduction. On the other hand, when using sodium acid carbonate as the original eelctrolyte in my process I successfully bubble gaseous CO2 through the bulk catholyte to maintain acid conditions and do so with no disturbance whatsoever of the alkaline film which has been set up at the cathode surface. This is real evidence that the alkaline film set up by me in an acid buffered solution as a result of positive steps taken to do so is inherently a more stable film than that which forms spontaneously during the electrolysis in a non-bufiering electrolytic solution of sulfuric acid and sodium sulfate.

I have carried out the process of my invention using buffered electrolytes with very good results while employing standard electrodes such as pure lead, amalgamated lead and amalgamated zinc as the cathode. None of these electrodes, however, was found to possess high mechanical strength over a period of continued use. My invention is also concerned, therefore, with novel,

mechanically strong and highly durable cathodes -and methods of preparing the cathode surfaces for successful use. I have found that nickel or .current efficiencies than any which, to my knowledge, have been reported in the electrolysis of acid For example, one current efficiency at reduction of glucose to sorbitol was 50%. The desired results are secured by first etching the surface of the metal electrode, for instance with acid, and then immersing the etched electrode in a bath of acid and a mercury salt until the metal acquires a shiny appearance. Thus I produce an electrode surface which will operate at high current efficiency and at the same time I have an electrode of real strength and durability. The advantages to be found in the use of strong, durable electrodes and in such a simple method of preparing an efficient surface are readily apparent. Further reference will be made, hereinafter, to the results obtained from the use of my improved electrodes. This subject matter, however, is claimed in my co-pending divisional application Ser. No. 225,269 filed May 8, 1951.

The characteristics of my invention will behest understood and appreciated from the following detailed description of a preferred procedure in carrying it out and as suggested in the accompanying description of the cell.

The cell used is of well known standard design and it will be understood that any desired or conveneint arrangement of the elements of the cell may be madewithin the scope of the process defined. The cathode consists of a metal plate and the anode may consist of plates, rods, mesh, etc. The volume of catholyte may best be described as consisting of 13 liters per 200 square decimeters of cathode plate, while the anolyte is of approximately the same ratio to anode surface. The anode is separated from the cathode by a diaphragm of porous Alundum of about 0.5 cm. wall thickness and a permeability of about 5 10- DArcys. The catholyte is confined to the space between the cathode plate and the diaphragm and the anolyte surrounds the anode. The distance between cathode surface and anode surface may vary upward from about 1.5 inches but in order to achieve high current efficiencies should not be much above 3 inches.

In preparing to carry out the process of my invention a solution of glucose or other sugar and electrolyte is introduced into the cathode compartment and a solution of electrolyte into the anode compartment. The porous diaphragm will allow the passage of ions under the influence of the electric current but in general hinder the diffusion of sugar molecules from the catholyte into the anolyte. The diffusion of sugar may be stopped by setting up electroendosmosis of anolyte into the catholyte compartment. Makeup anolyte is then added to the anode compartment as needed. 7

The concentration of sugar and electrolyte may be varied widely, but it has been found that /2 to 2 molar electrolyte salt in the catholyte and 200 to 325 grams per liter of sugar in the catholyte and an acid anolyte of 1 to 3 molar concentration gives satisfactory results. The ratio of metallic cation to anion, e. g. sodium to phosphate, is highest at the cathode surface, decreases sharplyin the bulk catholyte, and is lowest in theanolyte where the cation is predominately hydrogen. The anion initially need not be the samein anolyte and catholyte and the metallic cation may be soaeol an dium wpotassium,cor the i like. "Obviously a' 'pH -grad1ent-exists from -ca'thode= surface to anode surface and it follows the curve exhibited by the metallic cation to anion ratio,'being highest at the cathode surface, dropping sharply in the bulk catholyte' and being very low-in the acidanolyte.

Required "conditions; such as a :certain ipfi conductivity, etc. may beeffectedby varying the anolyte makeup.

The cathode consists of a metallic plate prefer'ably treated in the manner already outlined,

and the anode is'preferably of lead or lead dioxide. Theprocess'of =my=in-vention can =be carried out using pure lead or treated 'leadgvzinc,

nickel or galvanized =iron'-as"the"material of the cathode. The passageof electric cur-rent through the cell liberates hydrogenat *the cathode and this in turn combines chemically with glucose or other reducible 'sugar' to produce the correspond- 'taminated and capab1e:of operating at highem- .ciency. For example, :it has-been foundthat phosphate and carbonate ions areexceptionally advantageousin this respect. Sulphate saltsvare definitely inferior.

ofcthe sugar is. .likely .to cease because of the formation of a contaminating sulfide filmon .the cathodersurface resulting. from reduction of sulphate ion. I have discovered that by various methods of introducing depolarization .following the start of electrolysis, the reduction of. sugar can be carried-outat high. current efliciency with thebulk catholyte inacid condition using a variety of cathodeand electrolyte salts. It should be .clear that in this disclosure a distinction is made between electrolysis whichgoes on whenever current is. flowing through the cellproduclng hydrogen. formed at the cathode, and-thereduction which is the utilization ofthe hydrogen .formed at the cathode surface by electrolysis. By

depolarization is meant, herein, the setting up of an alkalinefilm at the cathode surfaceand the subsequent reduction of glucose by cathodic hy- "drogen; in other words, cathodic reduction'fol- 'sodlum hydroxide :isaaddedi ini-the '1 manner; sulgcsted, there-isi-a marked'sdecreasein the rates!!! evolutlon of 'the hydrogen gas which is immediatelyobservab-lesto the-eye. .Qntes'ting thesnH of: ltherbuikrcatholyte it is foundto :be practically unchanged. "For-example, this techniqueimayu-be used tozinitiate depolarization bywusing to12 molar sodlum' dihydrogen phosphate as the electrolyte in "the cathode "compartment. Thisrsalt gives a-distinctlyccid pH in solution-and then-pH of theibu'lk catholyte remains unchanged by :depolarization. l he-buffer action of this salt :iswof value inmaintalning the pH of lthebulk-catholyte when using this-procedure for depolarization.

Anothe very"effective method of depolarization consists in mixing sodium dihydrogen phosphate 'vith sodium hydroxide "in the" catholyte until ithe pH' of lth'e biilk ca'thdlyte is about6;5 but always lower than "7.0. 'IIhiS Produces a mixturecof NaH2PO4 and NazHPO4' in the cathodic solution. fihosphoric acid may be used in thmanolyte. Electrolysis is i started "with high it current density varying up to 2 amperes or more er square decicathode to startithe reductionwithouttanyother -provision for depolarization. 'Atthe same-time meter of cathode surface. Usually this high current idensity moves enough sodium to the electroendosmosis is set up,randwbyl the time reduction is well under way'ithefbulk catholyte'is at a'Iower-pH than theoriginal. a At thisxpoint current density may be decreased. tmslow up. or

- stop;electroendosmosis.

" is to makeup 1 molar sodium bicarbonatesolu- In sulphatetruns reduction lowing setting up of the alkaline film wheresugar facts as the depolarizing agent. "It is of course clear that any glucose which is tobe reduced must diffuse through the alkaline "film in order to rea'ct with the hydrogen being'generated' at the cathode surface. "Since alkali degradation of sugaris' fairly rapid at moderately elevatedtem- 'per-atures, the thickness of the alkaline filmsis of .importancezin "its relation to product quality.

The-setting up of. the alkaline film animrportant and:necessary step in thedepolarization l tionsin the catholyte. .The pI-I. of this solution is about 8. Upon commencingelectrolysis. the. depolarization --takes aplace spontaneously rafter whichicarbon; dioxideis bubbledintothe catholyte until there is a positive excess of CO2 in the solution. This, of courseuinsurestheiacidity'rof-ithe bulk; catholyteand its .pH drops to .between 6 and 7. Carbon dioxide is bubbled into thecatholyte in. suflicientwamount to insure saturation ofithe bulk .tcatholyte as long as reduction continues. Tova-void: wastecf C(Dz, however, phosphoric acid mayrbe used in the anolyte; high current density impressed-lat the start, i and the, bulk .catholyte acidified by the electroendosmosis .of phosphoric acid into the catholyte. .In. thiscase the sodium bicarbonate acts .merely as an .aid to depolarizationaandthe anion-is replaced by the phosphate anion. In. the...same general :mannen-sodium. dibasioi-phosphate, NaiHPQa. can beused.

. Stills a further procedure which may. be used forldepolarization when the cathode=isrnot a mercury treated metal at" the start of electrolysis,

.iswzto. raddraxsmalls-amount. .mercury. saltsto-rthe anodencompertment. In a cell which otherwise cannot be made to ,depolarize satisfactorily the movementiof-thewmercury ions to thecathode is followed by: a marked decrease. in hydrogen; gas evolution and reduction of the sugar beginsato "teke..-place. .-The.additiomof=-the=mercury salt to the-lanolyte simply. insures perfect distribution-cs theions move tolsthe cathode; obviously/the salt can be addedt-tot-the catholyteuitself.

.--Although= @electroendosmosis is useful-in this technique and is wparticularly:effective,- it will be understooda-that: any. method loft acidifying .the bulk .catholyte asedesired maybe employed,.such

..as.'=.ther-.eddition. of. acid to the "03111101371763.4111 the regiomofithe-diaphragmorin .the bulk; but never directly at the cathode surface.

innce (depolarization-sis .establishedand rthezreduction is under way, it is possible to run quite high currentdensity, fora short time withoutup achieved readily 'by electroendosmosis .of acid fromthe anolyte; By using sodium phosphates and sodium bicarbonate as anionic buffers-it has been founda temperaturelevel of l0-50 in; the bulk-cathfol-yte is permissible for severalhours with the' production of water white catholytes.

Probablythe. explanation of this fact is thata thinner alkaline film is formed at the cathode surface with consequent lessening of the degradation of glucose diffusing through it to the cathode surface. 1 The following table is illustrative of typical runs of the process of my invention:

For example, it ispossible .to

lowed to plate out at room temperature until the cathodehas a shiny appearance, after which the cathode is washed in water and is ready for use. J;

The advantages of such a simple method of mercury treating the cathode are obvious since no handling of liquid mercury is entailed and the amount of mercury plated out can be controlled exactly by regulating the time of immersion in the bath. The mercuric nitrate dissolves readily in fairly concentrated nitric acid and can then be diluted as desired. The bath can be used over and over provided the mercury used is replaced. The cathode material must at all times be,

handled with care and the surface protected from roughing, chemical action, etc. I i

I purposely call this cathode preparation a mercur treatment rather than an amalgamation because even a short treatment which does not leave the cathode with an amalgamated appear-. ance will result in satisfactory reduction. I have pointed out previously that just traces of mercury will depolarize a pure metal cathode, lead Table I Glucose (latholyte Anolyte a I: Operat- Gathol te Per Cent 0. E. Oathol te No. conc. Make-up Make-up Cathode 10 D T I? 0' ing Hours plil S. R. Per Cent Appearance ji;, i g i: :}af3MH3l O Q i Prim..- 0. 70 -45 22% 4-5 76 43 water white.

.1320 6%? do Pb-Hg 0.70 40-45 42 5-6 99 52 Do. 3;.-." I 320{ do do 0.70 40-45 42 5-6 99 55 Do.

v 325 .do z -H 0.50 40 24 4-5-6 92 66 Do.

eiuebse concentration is in grams of glucose (anhydrous) per liter of solution.

'Catholyte make-up is initial concentration of electrolyte per liter of solution in mols of electro-' lyte." v Anolyte make-up is the same. A

Cathode refers to themetal (or-treated metal) plate used.

C. D. is current density in' amperes per square decimeter of cathode surface. This is given to represent approximately the average operating the cell. A range of 2-7 pH was found perfectly operable." Y I Percent S. R. is percent sugar reduction'as de-- termined by Fehlings test using the Lane and Eynon method.

C. E. percent-is current efficiency at the percent S. R. given as determined from the Fehlings tests.

The following is a description of my'method of preparing the cathode surfaces. In the case of pure lead, the use of nitric acid of such strength as to etch the metal surface is sufficient. This is approximately 6 N, but a wide variation in concentration is permissible provided the etching is thorough. This is, of course, followed by a water wash. In the case of the Pb-H g or Zn-'-'Hg cathode, the cathode is first rinsed in the dilute nitric and then in water, following which the complete cathode is immersed in a dilute nitric acid-mercuric nitrate bath. The" mercury is alfor example. The cathode of run No. 1 was pure lead however, depolarized with dilute sodium hydroxide solution. The ease and economy of such a method of cathode preparation results in a considerable improvement over the traditional method'of rubbing mercury into the lead or zinc surface by hand with consequent variations in the degree of amalgamation over various sec 'tions of the metal surface and severe weakening of the metal. Lead and zinc cathodes even when prepared by this mercury treatment embrittle with age and lose most of their mechanical strength in time. However, I have developed mechanically enduring cathodes which operate at high current efliciencies in bufiered acid catholytes. As the cathode material I use a metal which is mechanically strong, which is substantially insoluble in mer cury and highly resistant to its weakening effect but which is capable, either directly or indirectly of superficial surface malgamation, the amalgaimated surface being extremely thin but. highly perfect in surface structure. This, of course, 8X? cludes the use of lead which is mechanically weak, copper which is weak and highly soluble in mercury, and zinc which is also highlysoluble in mercury. One of the cathodes discoveredby me is nickel, etched in concentrated nitric acid and then mercury treated. Iron can also be used but I prefer to first galvanize before mercury treating. The reason for thisis that the overvoltage of iron is low and that of zinc is high and is well known that by the process of hot dipping a very thin and highly perfect zinc coat can be formed on the iron. I prefer to first form and etch'the galvanized iron electrode and then redip it in molten zinc near the melting point, reetch and then mercury treat. This produces a relatively thick zinc-mercury coating and coats all exposed edges. Either electrode serves the purpose of producing lasting internal strength and high current efficiencies, but nickel is to be preferred. in spite of its higher cost because of the ease of handling and the higher current efficiencies obtainable from its use.

Table II Run Glucose Catholyte Auolyte Operat- Catholyte Per Cent 0. E. Catholyte N o. cone. Make-up Make-up Cathode T o int, Hours pH S. R. Per Cent Appearance 325 {igffifgg }2s MH3PO4.. 0.65 Ni-Hg 4o 24 4-5-6-7 95 50 Water white. 6 325 1 M NaHOO3 1 M NaHOO3 0.50 do 50 3 67 30 very high lightyellow. 320 {i iffigg }2-3 M Harolfl 1. 0 (3?. iron 40-45 22% 5-6 76 43 water white.

In run No. 6 carbon dioxide was bubbled into the catholyte during reduction in order to maintain acidity there. There was at all times an excess of CO2 in the sugar solution.

Having thus disclosed my invention and described in detail various illustrative ways of practicing it, I claim as new and desire to secure by Letters Patent:

1. A process of producing a polyhydric alcohol in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, which comprises the steps of maintainin in the cathode compartment an acid solution at pH not less than 2.5 of the sugar corresponding to the said alcohol together with a buifer salt of a Weak acid and an alkali metal, the anions of which are irreducible at the oathode under the conditions imposed, maintaining an acid anolyte of pH 0 to 7 in the anode compartment, flowing an electric current through the cell at a density of not over 4 amp/sq. dec., forming an alkaline film at the cathode, and causing the sugar to pass through the alkaline film to the cathode and to be reduced to alcohol by hydrogen liberated at the cathode.

2. The process defined in claim 1 further characterized by the employment of phosphate anion in the acid anolyte and in the acid catholyte.

3. The process defined in claim 1 further characterized by the employment of carbonate anion in the acid anolyte and in the acid catholyte.

4. The process defined in claim 1 further characterized by the employment of carbonate anion in the acid catholyte and phosphate anion in the acid anolyte- 5. The process defined in claim 1 further characterized by the employment of electroendosmosis to control pH in the bulk catholyte.

6. The process defined in claim 1 further characterized by the control of pH in the bulk catholyte by varying the intensity of electric current through the cell and the amount of electroendosmosis induced thereby.

7. The process defined in claim 1 further characterized by the step of applying liquid alkali to depolarize a cathode immersed in acid catholyte.

sis to establish depolarization of the cathode surface.

10. The process defined in claim 1 further characterized by the step of depolarizing the cathode by adding sodium bicarbonate to the catholyte- 11. The process defined in claim 1 further characterized by the steps of addin gaseous C02 to the catholyte, saturating the same therewith and maintainin it in acid condition therewith, while using carbonate anion therein.

12. A process of producing sorbitol in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, which comprises the steps of maintaining in the cathode compartment an acid solution of glucose and a bufier salt of a weak acid and an alkali metal at a pH not less than 2.5, the anions of which are irreducible at the cathode under the conditions imposed, maintaining an acid anolyte of pH 0 to 7 in the anode compartment, flowing an electric current through the cell at a current density of not more than 4 amps/sq. dec., forming an alkaline film at the cathode, and causing the glucose to pass through the alkaline film to the cathode and to be reduced to sorbitol by hydrogen liberated at the cathode.

CHERRY L. EMERSON, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,094,315 Earle et al Apr- 21, 1914 1,094,316 Earle et a1 Apr. 21, 1914 1,324,835 McCoy Dec. 1 6, 1919 1,938,961 Gravell Dec. 12, 1933 1,990,582 Creighton Feb. 12, 1935 2,300,218 Hales Oct. 27, 1942 OTHER REFERENCES Ser. No. 276,706, Grandel (A.P.C.), published May 18, 1943.

Wilson et al.: Transactions Electrochemical Society, vol. 80, (1941). pp. 139-150. 1 

1. A PROCESS OF PRODUCING A POLYHYDRIC ALCOHOL IN AN ELECTROYLTIC CELL HAVING ANODE AND CATHODE COMPARTMENTS SEPARATED BY A PERMEABLE DIAPHRAGM, WHICH COMPRISES THE STEPS OF MAINTAINING IN THE CATHODE COMPARTMENT AN ACID SOLUTION AT PH NOT LESS THAN 2.5 TO THE SUGAR CORRESPONDING TO THE SAID ALCOHOL TOGETHER WITH A BUFFER SALT OF A WEAK ACID AND AN ALKALI METAL, THE ANIONS OF WHICH ARE IRREDUCIBLE AT THE CATHODE UNDER THE CONDITIONS IMPOSED, MAINTAINING AN ACID ANOYLET OF PH 0 TO 7 IN THE ANODE COMPARTMENT, FLOWING AN ELECTRIC CURRENT THROUGH THE CELL AT A DENSITY OF NOT OVER 4 AMP./SQ. DEC., FORMING AN ALKALINE FILM AT THE CATHODE, AND CAUSING THE SUGAR TO PASS THROUGH THE ALKALINE FILM TO THE CATHODE AND TO BE REDUCED TO ALCOHOL BY HYDROGEN LIBERATED AT THE CATHODE. 